The Effect of Aloe Vera, Pomegranate Peel, Grape Seed Extract, Green Tea, and Sodium Ascorbate as Antioxidants on the Shear Bond Strength of Composite Resin to Home-bleached Enamel.

Statement of the Problem Immediate application of bonding agent to home- bleached enamel leads to significant reduction in the shear bond strength of composite resin due to the residual oxygen. Different antioxidant agents may overcome this problem. Purpose This study aimed to assess the effect of different antioxidants on the shear bond strength of composite resin to home-bleached. Materials and Method Sixty extracted intact human incisors were embedded in cylindrical acrylic resin blocks (2.5×1.5 cm), with the coronal portion left out of the block. After bleaching the labial enamel surface with 15% carbamide peroxide, they were randomly divided into 6 groups (n=10). Before performing composite resin restoration by using a cylindrical Teflon mold (5×2 mm), each group was treated with one of the following antioxidants: 10% sodium ascorbate solution, 10% pomegranate peel solution, 10% grape seed extract, 5% green tea extract, and aloe vera leaf gel. One group was left untreated as the control. The shear bond strength of samples was tested under a universal testing machine (ZwickRoell Z020). The shear bond strength data were analyzed by one-way ANOVA and post hoc Tukey tests (p< 0.05). Results No significant difference existed between the control and experimental groups. Moreover, there was no statistically significant difference between the effects of different antioxidants on the shear bond strength of bleached enamel. Conclusion Different antioxidants used in this study had the same effect on the shear bond strength of home-bleached enamel, and none of them caused a statistically significant increase in its value.


Introduction
Vital tooth bleaching generally involves application of hydrogen peroxide on the tooth surface in an office technique or application of carbamide peroxide in home technique. [1][2] Carbamide peroxide and hydrogen peroxide function as oxidative agents by forming free radicals, oxy-gen reactive molecules, and hydrogen ions. These active molecules attack the pigments that are present in the teeth and remove them; the reason we can observe their effectiveness in whitening of the teeth. [3][4][5] In home bleaching technique, carbamide peroxide is used for 0.5-8h/day depending on its concentration under a dentist's supervision. [3][4][5] Bleaching treatment leaves some side effects on the teeth namely decreasing the bonding ability, causing morphological changes in enamel and dentin surface, reducing enamel wear resistance, and causing surface roughness. It also increases enamel porosity and changes the enamel and dentin mechanical features such as fracture toughness which may reduce the tooth crack resistance and strength. [6] The shear bond strength (SBS) of composite resin bonded to the tooth surface decreases dramatically right after bleaching treatment. This reduction in SBS is related to the residual peroxides, the presence of which interfere with resin tag formation and the resin bond to the tooth, and subsequently impede the polymerization of resin monomers. The rest of oxygen disperse gradually, and after an appropriate time period (24 hours to 4 weeks), the composite resin recover its bond strength. [7][8][9] There are some techniques to prevent the reduction of composite resins bond strength after bleaching, such as removing superficial enamel and application of adhesives which contain organic solutions, alcohol, or antioxidants. [2,[8][9] Application of antioxidants was reported to be a reversal in the decline of SBS of composite resin to bleached enamel due to its protective role against free radical reactions. [10] Sodium ascorbate, grape seed extract, green tea, pomegranate peel extract, and aloe vera are some antioxidants. [8][9][11][12][13] Sodium ascorbate is a neutral, nontoxic and biocompatible antioxidant that improves the bond strength of bleached enamel. [10] The grape seed extract contains oligomeric proanthocyanidin complex which is more potent than sodium ascorbate. Antioxidant activity of dry green tea leaves is related to flanavols. [6,[14][15] Pomegranate peel extract contains effective compounds such as polyphenols whose antioxidant benefits preponderate over green tea. Likewise, the antioxidant effect of aloe vera is attributed to the polysaccharides found in the leaf gel. [7,[11][12][13] Sasaki et al. showed that 10% sodium ascorbate could not reverse the oxidizing effect of 10% carbamide peroxide on enamel and could not increase the SBS.
[10] However, in another study, carbamide peroxide bleaching was followed by application of sodium ascorbate hydrogel and it was found to have increased the SBS of bleached enamel, which was proportional to the duration of application. [16] No published study has compared the effectiveness of different antioxidants on the SBS of homebleached enamel. The aim of this in-vitro study was to evaluate and contrast the effects of different antioxidants, including aloe vera, green tea, pomegranate peel extract, grape seed extract, and sodium ascorbate on the SBS of home-bleached enamel.

Materials and Method
In this experimental study, 60 recently extracted sound human maxillary incisors were collected and randomly pomegranate peel extract solution, 10% grape seed extract solution, and 5% green tea solution, respectively.
Aloe vera gel was prepared from the aloe vera inner leaf. The study groups were named alphabetically from A to F. In group A (control group), immediately after bleaching, composite resin restorative procedure was carried out. In groups B, C, D, and E immediately after bleaching, a solution of 10% sodium ascorbate, 10% pomegranate peel, 10% grape seed extract, 5% green tea, and aloe vera leaf gel were respectively applied on the bleached enamel surface for 10 minutes. Then the samples were rinsed with water for 30 seconds and

Results
The values of Mean±SD shear bond strength of all the 6 groups are represented in Table 1.
ANOVA was used to analyze the differences between the mean SBS of study groups, and Tukey's posthoc test was used to determine the significant differ-ences between the mean values of the groups. One-way ANOVA revealed no statistically significant difference between the control group and groups treated with antioxidants (p< 0.05). Similar mean values were obtained from the groups treated by different antioxidants ( Figure   2).